Egyptians have voted in a key referendum on constitutional changes, which the opposition criticise as paving the way for a police state.

The information minister put turnout at between 23% and 27%, but unofficial estimates were much lower.

The 34 amendments include a ban on the creation of political parties based on religion, and sweeping security powers.

The government says the changes will deepen democracy, but opponents say it will be easier to rig future elections.

Some independent groups monitoring the poll put the turnout figure at 5% or less.

They say that voting stations stood empty for most of the day in many places, and that in some areas the authorities bussed in public sector workers and government employees to ensure a reasonable turnout.

But correspondents say there has been little sign of the "millions of voters heading to ballot boxes" reported by the official news agency, Mena.

The BBC's Heba Saleh in Cairo says that if voters stayed away it was not because of opposition calls for a boycott but because Egyptians feel their votes do not count.

"What's the use? All referendums are fixed," said one taxi driver quoted by AFP news agency.